Biosolids are the solid, semi-solid, or liquid residue generated during the biological wastewater treatment process. Biosolids for beneficial use (i.e. land application, marketing or distribution) must be treated to reduce pathogens and vector attraction (“VAR”).
Insects, birds, rodents, and domestic animals may transport sewage sludge and pathogens from sewage sludge to humans. Vectors are attracted to sewage sludge as a food source, and the reduction of the attraction of vectors to sewage sludge to prevent the spread of pathogens is a focus of federal regulation. VAR can be accomplished in two ways: by treating the sewage sludge to the point at which vectors will no longer be attracted to the sewage sludge or by placing a barrier between the sewage sludge and vectors.
After the treatment of wastewater is performed, the generated biosolids needs to be beneficially reused or disposed. Generally, biosolids are hauled from wastewater treatment plants and beneficially reused in rural farm areas where biosolids are applied to farm fields or are transported to a landfill for disposal. Large volumes of sludge (biosolids) create large transportation expenses. Wastewater sludge contains relatively high percentage of water, and large volumes are created for transport out for reuse or disposal. The sludge also can create environmental and or health problems.
Federal, state and local governments regulate the distribution and marketing of Class A biosolids. Class A biosolids represent the highest quality biosolids produced and may be used as fertilizer through commercial distribution and marketing. To achieve a Class A status, the biosolids must be treated to a level that essentially nearly eliminates pathogens and must meet stringent maximum concentration limits for heavy metals. Class A biosolids may be distributed in bulk or bagged for sale at retail centers. Class A biosolids may be marketed in different physical forms, and, like traditional commercial fertilizer, are not subject to site management restrictions if the product is registered as a fertilizer or distributed and marketed to a person or entity that will sell or give-away the biosolids (wholesale) or market biosolids products as a fertilizer (retail).
The United States Environmental Protection Agency's (EPA) Regulations recognize at least two classes. Class B pathogen reduction standards, as set forth in 40 C.F.R. 503, require a fecal coliform level of less than two million most-probable-numbers (MPN) per gram of total solids. Class A pathogen standards, (40 C.F.R. 503) require fecal coliform densities are less than 1,000 MPN per gram total solids; or when Salmonella densities are less than 3 MPN per four grams total solids. Additionally, enteric virus must be less than 1 plaque-forming unit per four grams of total solids, and helminthes ova must be less than one viable helminthes ova per four grams of total solids.
Traditionally, biosolids disposal involves trucking the sludge to rural areas and applying the sludge onto fields. This process increases health and environmental concerns. Other methods of disposal may include incineration, adding chemicals, or disposal into landfills. Concerns about contaminants, runoff, air pollution, tipping fees, and rising transportation costs have resulted in cities and municipalities seeking alternate, more efficient methods to handle the removal of biosolids.